Summary

Six triprenyl phenols that inhibit the in vitro binding of 3H-SCH 23390 to the dopamine D1receptor subfamily in rat striatal brain membranes were isolated from extracts of the edible mushroom Albatrellus ovinus. The compounds, of which scutigeral 1a, ilicicolin B 3, neogrifolin 5a and grifolin 6 are known while ovinal 2 and ovinol 4a are new, were isolated by chromatography and their structures were determined by spectroscopic techniques. The IC50values of the most potent compound, scutigeral 2a, is 2.6 M and it was shown that it decreases the binding affinity of 3H-SCH 23390 in a competitive manner. Compounds 1–5showed no inhibition on the binding of 3H-spiperone to the dopamine D2receptor subfamily, indicating that these compounds interact selectively with the dopamine D1receptor subfamily.

Abstract

1. A [3H]-resiniferatoxin (RTX) binding assay utilizing rat spinal cord membranes was employed to identify novel vanilloids in a collection of natural products of fungal origin. Of the five active compounds found (scutigeral, acetyl-scutigeral, ovinal, neogrifolin, and methyl-neogrifolin), scutigeral (Ki=19 microM), isolated from the edible mushroom Albatrellus ovinus, was selected for further characterization. 2. Scutigeral induced a dose-dependent 45Ca uptake by rat dorsal root ganglion neurons with an EC50 of 1.6 microM, which was fully inhibited by the competitive vanilloid receptor antagonist capsazepine (IC50=5.2 microM). 3. [3H]-RTX binding isotherms were shifted by scutigeral (10-80 microM) in a competitive manner. The Schild plot of the data had a slope of 0.8 and gave an apparent Kd estimate for scutigeral of 32 microM. 4. Although in the above assays scutigeral mimicked capsaicin, it was not pungent on the human tongue up to a dose of 100 nmol per tongue, nor did it provoke protective wiping movements in the rat (up to 100 microM) upon intraocular instillation. 5. In accord with being non-pungent, scutigeral (5 microM) did not elicit a measurable inward current in isolated rat dorsal root ganglion neurons under voltage-clamp conditions. It did, however, reduce the proportion of neurons (from 61 to 15%) that responded to a subsequent capsaicin (1 microM) challenge. In these neurons, scutigeral both delayed (from 27 to 72 s) and diminished (from 5.0 to 1.9 nA) the maximal current evoked by capsaicin. 6. In conclusion, scutigeral and its congeners form a new chemical class of vanilloids, the triprenyl phenols. Scutigeral promises to be a novel chemical lead for the development of orally active, non-pungent vanilloids.

Source

Abstract

Three neogrifolin derivatives, 3-hydroxyneogrifolin, 1-formylneogrifolin and 1-formyl-3-hydroxyneogrifolin along with grifolin and neogrifolin were isolated from the Japanese mushroom Albatrellus ovinus belonging to Scutigeraceae. Their structures were established by a combination of two-dimensional NMR spectroscopic analyses and by chemical synthesis. 3-Hydroxyneogrifolin and 1-formyl-3-hydroxy-neogrifolin showed more potent antioxidative activity properties than either alpha-tocopherol or BHA.